Neutral Current and the Onset of the Helium Flash

Ramadurai, S.

doi:10.1093/mnras/176.1.9

Cited by 17 publications

(10 citation statements)

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“…Nuclear reaction rates are taken from Angulo et al (1999) with screening corrections from Salpeter & van Horn (1969) and Itoh et al (1979). Neutrino loss rates are from Beaudet, Petrosian & Salpeter (1967) with modifications for neutral currents (Ramadurai 1976). Plasma neutrino rates are from Haft, Raffelt & Weiss (1994).…”

Section: Stellar Models and Physics Inputmentioning

confidence: 99%

Synthetic stellar populations: single stellar populations, stellar interior models and primordial protogalaxies

Jiménez

MacDonald

Dunlop

et al. 2004

Monthly Notices of the Royal Astronomical Society

121

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We present a new set of stellar interior and synthesis models for predicting the integrated emission from stellar populations in star clusters and galaxies of arbitrary age and metallicity. This work differs from existing spectral synthesis codes in a number of important ways, namely (1) the incorporation of new stellar evolutionary tracks, with sufficient resolution in mass to sample rapid stages of stellar evolution; (2) a physically consistent treatment of evolution in the Hertzsprung–Russell (HR) diagram, including the approach to the main sequence and the effects of mass loss on the giant and horizontal branch phases. Unlike several existing models, ours yield consistent ages when used to date a coeval stellar population from a wide range of spectral features and colour indexes. We use Hipparcos data to support the validity of our new evolutionary tracks. We rigorously discuss degeneracies in the age–metallicity plane and show that inclusion of spectral features blueward of 4500 Å suffices to break any remaining degeneracy and that with moderate S/N spectra (10 per 20‐Å resolution element) age and metallicity are not degenerate. We also study sources of systematic errors in deriving the age of a single stellar population and conclude that they are not larger than 10–15 per cent. We illustrate the use of single stellar populations by predicting the colours of primordial protogalaxies and show that one can first find them and then deduce the form of the initial mass function (IMF) for the early generation of stars in the Universe. Finally, we provide accurate analytic fitting formulae for ultrafast computation of colours of single stellar populations.

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Section: Stellar Models and Physics Inputmentioning

confidence: 99%

Synthetic stellar populations: single stellar populations, stellar interior models and primordial protogalaxies

Jiménez

MacDonald

Dunlop

et al. 2004

Monthly Notices of the Royal Astronomical Society

121

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“…Nuclear reaction rates are taken from Fowler, Caughlan, & Zimmerman (1975), Harris et al (1983), Nomoto, Thielemann, & Miyaji (1985), Caughlan & Fowler (1988), and Arnett (1996), and screening corrections are from Salpeter & Van Horn (1969) and Itoh et al (1979). Neutrino loss rates are from Beaudet, Petrosian, & Salpeter (1967) with modifications for neutral currents (Ramadurai 1976). Plasma neutrino rates are from Haft, Raffelt, & Weiss (1994).…”

Section: Description Of the Stellar Evolution Programmentioning

confidence: 99%

Sakurai’s Object, V605 Aquilae, and FG Sagittae: An Evolutionary Sequence Revealed

Lawlor

MacDonald

2003

ApJ

103

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We have completed a grid of stellar evolution calculations to study the behavior of the born-again phenomenon. All our evolutionary sequences begin with a uniform composition 1 M star on the pre-main-sequence Hayashi phase and end on the white dwarf cooling track. The effects of combined helium and hydrogen burning and time-dependent convective mixing are included. We artificially vary the mass-loss rate beginning at the peak of the last thermal pulse on the asymptotic giant branch in order to create a range of He-layer masses for the post-asymptotic giant branch (AGB) evolution. We find that a very late thermal pulse occurs in 10%-15% of cases. Our models supply an answer to the question of why the born-again stars V4334 Sgr (Sakurai's object) and V605 Aql have a significantly shorter evolutionary timescale than the otherwise similar bornagain star FG Sge. FG Sge has been observed to undergo born-again behavior for more than 120 yr, while the other two objects have evolved in a similar way but in less then 10 yr. Models with low convective mixing efficiency, $10 À4 , first evolve quickly to the AGB, return to the blue, and then evolve more slowly back to the AGB for a second time before finally returning to the white dwarf cooling track. The difference in evolution timescales can then be explained by proposing that Sakurai's object is evolving to the AGB for the first time but that FG Sge has been observed during its second return to the AGB. Our models allow us to make some testable predictions: (1) Sakurai's object will increase in effective temperature in the next 20-50 yr and will then resemble V605 Aql's present high effective temperature state; (2) V605 Aql will cool back toward the AGB some time in the next 50-70 yr, at which point it will evolve in the same way as has been observed for FG Sge over the last 120 yr; and (3) FG Sge will show signs of increasing its effective temperature by about 1500-2000 K in as soon as 10-20 yr, depending on the metallicity of its progenitor main-sequence star.

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“…The SG78 calculations, in particular, neglect neutral-current e ects (Weinberg 1967;Salam 1968), which may have led to an underestimate of their M c values (Ramadurai 1976; SG78).…”

Section: Standard Neutrino Lossesmentioning

confidence: 99%

The Helium-Core Mass at the Helium Flash in Low-Mass Red Giant Stars: Observations and Theory

Catelan¹,

Pacheco²,

Horvath³

1996

ApJ

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The method developed by Ra elt (1990a,b,c) to estimate a possible increase in the standard values of the helium-core mass at the tip of the red giant branch, M c , from properties of the color-magnitude diagrams of Galactic globular clusters is employed. In the present study, we revise and update Ra elt's database, including also constraints from RR Lyrae pulsation, and nd that a small increase, by M c 0:01 0:015 M , cannot be ruled out with the present data and evolutionary models. Our new upper limits on M c are less restrictive than those previously obtained by Ra elt, as are the corresponding constraints on novel astroparticle phenomena which may a ect the evolution of low-mass red giants. Within the estimated uncertainties, however, the standard values of M c may also be acceptable. Ra elt's method does not rule out a low envelope helium abundance in globular cluster giants, though again the standard values are compatible with the available constraints. The in uence of a non-solar ratio for the -capture elements upon these results is also investigated. In addition, we review several aspects of the input physics employed in red giant stellar evolutionary calculations, with the purpose of evaluating possible sources of uncertainty in the value of the helium-core mass at the helium ash that is obtained from evolutionary computations, such as: heat conduction by electrons in the degenerate core; Coulomb e ects upon the Equation of State; triple-reaction rates and screening factors; neutrino emission rates, both standard and enhanced by a possible non-zero magnetic moment; stellar rotation; microscopic element di usion; and energy losses by axions and Weakly Interacting Massive Particles.

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Neutral Current and the Onset of the Helium Flash

Cited by 17 publications

References 0 publications

Synthetic stellar populations: single stellar populations, stellar interior models and primordial protogalaxies

Synthetic stellar populations: single stellar populations, stellar interior models and primordial protogalaxies

Sakurai’s Object, V605 Aquilae, and FG Sagittae: An Evolutionary Sequence Revealed

The Helium-Core Mass at the Helium Flash in Low-Mass Red Giant Stars: Observations and Theory

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